1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording densities of hard disk drives. In particular, the areal recording densities of the latest hard disk drives have reached 100 to 160 gigabytes per platter and are even exceeding that level. It is required to improve the performance of thin-film magnetic heads, accordingly.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording (write) head having an induction-type electromagnetic transducer for writing and a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
Typically, the write head incorporates: a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of a medium facing surface (an air bearing surface) that faces toward a recording medium; a write gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers.
Typically, the read head has a structure in which the MR element is disposed between a bottom shield layer and a top shield layer.
A flying-type thin-film magnetic head used in a hard disk drive, for example, is typically made up of a slider having a thin-film magnetic head element formed in the trailing edge. The slider is slightly lifted above the surface of a recording medium by means of an air flow generated by rotation of the medium. To improve the areal recording density of the hard disk drive, it is required to reduce the height at which the slider flies. The distance between the thin-film magnetic head element and the surface of the recording medium is about 5 to 8 nanometers (nm), for example, when the slider is flying.
If the height at which the slider flies is reduced, it is likely that the slider collides with the recording medium, and the head element or the medium thereby suffers damage. Moreover, in the write head, the pole layers expand because of the heat generated by the thin-film coil and the medium-facing-surface-side ends of the pole layers protrude in some cases. Such protrusion of the pole layers increases the occurrences of the collision of the slider with the recording medium.
In composite magnetic heads, the bottom pole layer is located closer to the read head than the top pole layer, and the top pole layer defines the write track width. In addition, the bottom pole layer is often made greater in size than the top pole layer. In such a case, the amount of expansion of the bottom pole layer due to the heat is greater than that of the top pole layer since the bottom pole layer is greater in volume. Moreover, the bottom pole layer is located farther from the surface of the slider than the top pole layer, so that the heat of the bottom pole layer is hard to release to the outside. This is another reason that the amount of expansion of the bottom pole layer due to the heat increases. As thus described, the volume of protrusion of the bottom pole layer is likely to increase.
To reduce the amount of protrusion of the bottom pole layer, a reduction in size of the bottom pole layer is considered. However, if the bottom pole layer is reduced in size, it is difficult that the heat conveyed from the coil to the bottom pole layer is released from the bottom pole layer. As a result, the volume of expansion of the bottom pole layer due to the heat increases, and the volume of protrusion of the bottom pole layer increases, too.
If the bottom pole layer also functions as the top shield layer of the read head, a reduction in size of the bottom pole layer causes a problem that the function of shielding the MR element is reduced and the characteristic of the read head is reduced.